The invention relates to a circuit arrangement for noise reduction at the minimum volume setting of a low-frequency amplifier which includes a switching circuit for varying the volume dependent on a direct control voltage which can be varied by a volume control means.
In low-frequency amplifiers a disturbing intrinsic noise of the amplifier often occurs in the case of minimum volume setting. The intrinsic noise is particularly strong when an active integrated switching circuit for setting the volume and the tone is used whose intrinsic noise becomes particularly audible in a disturbing manner in the case of minimum volume setting of the amplifier.
Circuit arrangements for low-frequency amplifiers are known in which the volume control is carried out at several points in the amplifier. The volume control means used in the circuit arrangement has several potentiometers which are connected into several stages of the amplifier. In such circuit arrangements the amplifier must additionally be designed for multi-stage volume control and this required relatively many cable connections between the potentiometers and the amplifier. The construction of the circuit is thus relatively complicated and eliminates the advantages of the very simple circuit construction of an active integrated switching circuit for volume control.
A receiver for high-frequency magnetic oscillations using gain control and a monitoring circuit is known from DE-OS No. 24 60 602 in which a control voltage is obtained in the automatic gain control circuit in order to control a switching amplifier connected to a switch-off device arranged in the path of the output signal. The output signal of the receiver is thus muted when the reception level comes below a given value. A corresponding control voltage of an automatic gain control is used as a criterion for the value of the reception level. This circuit is thus used to mute the output when the input signal of the RF receiver becomes too weak. Similar circuits are also known in other embodiments and are generally referred to as muting circuits.